use second character of symbol name in wrap_special

attempt to avoid unnecessary strcmp calls, and when we do call it, be as
efficient as possible with it.

Signed-off-by: Jeremy C. Andrus <jeremya@cs.columbia.edu>
first-pass at finding identical stacks in backtrace

This doesn't seem to quite work, but also doesn't break the backtracing,
so I am committing it :-)

Signed-off-by: Jeremy C. Andrus <jeremya@cs.columbia.edu>